Mary Down Hahn grew up in Newark, Maryland. In elementary school, she was an artist. She loved reading and drawing, but hated writing. However, she loved to tell stories, but as a young girl she told the stories through pictures.

By junior high, she wanted to create more intricate stories, and that is when she started writing, along with illustrating. She wrote her first book called, Small Town Life, during this time. She never finished it, but she continued writing. In high school, she did this by writing in a journal. In college, she created poetry with the hopes of being published in The New Yorker. Unfortunately, she lacked the confidence to read and write.

She was a children's librarian before she decided to write and release her first book, The Sara Summer. After writing The Sara Summer,she started averaging one book a year. To date, she has released many renowned novels for children, including winning the Scott O'Dell award for the book Stepping on the Cracks. The is a three time winner of the William Allen White Children's Book Award.